Is there room to get in there with a hand held mallet of some description and tap the two groups of bars manually? It would be nice to be able to rule out the mechanism, so we only have to worry about the bars.

What locates the bars in the horizontal plane? Are there pins through vertical holes in the bars or some similar locating device? Or strings through horizontal holes? Are the dull bars free to move a little horizontally as well as vertically?